COLUMBIA, Md. – Investigators probing slain federal prosecutor Jonathan Luna’s grisly death are zeroing in on the details of his personal life – including possible sex solicitations via the ‘Net, mystery trips to Pennsylvania and a credit card his wife didn’t know about.

Law-enforcement officials familiar with the probe into the slaying of the Bronx-born assistant U.S. attorney said yesterday they are focusing increasingly on the theory that his murder was the result of a personal relationship gone awry, rather than a random robbery or something connected to his work as a drug prosecutor in Maryland.

FBI agents and Pennsylvania state police are interviewing friends and relatives, as well as canvassing hotels around Lancaster County, Pa., near where Luna’s body was found Thursday.

Luna died after being stabbed 36 times, apparently tortured with a pen knife, authorities said.

Investigators discovered that in recent weeks, Luna had made at least two other unexplained trips to the area that do not appear to have been work-related.

His father, Paul Luna, said that his son just last week canceled a trip they had planned to make to New York this past weekend. The elder Luna said his son told him he couldn’t make the trip because he had business in Pennsylvania.

In the aftermath of his death, Luna, 38, has been portrayed by friends and colleagues as a hard-working lawyer and devoted family man who rose from the projects of the South Bronx to a promising career in law enforcement.

But investigators say that friends privately told them after his death that he seemed distracted and stressed out at work in recent months.

Law-enforcement sources said they also have discovered he had a credit card that his wife didn’t know about.

The FBI is also examining postings on adult Web sites in which a man by Luna’s name is seeking female sex partners.

Although law-enforcement officials say they aren’t sure Luna actually posted them, The Post examined one made in 1997 in which the man looking for sex describes himself as a then-31-year-old lawyer living in Brooklyn.